Imperial reported a spill to the St. Clair River that required downriver notification Tuesday afternoon.
Sarnia Police Dispatch first relayed a message from the company just after 1 p.m.
In its notice, Imperial said its water treatment [facility] had a minor carryover of biomass to the river.
"This occurred this morning and [was] contained within the site’s outfall," Imperial said in a message a few minutes later from Sarnia-Lambton Alerts. "Booms have been placed within that area of the river. This has been reported to the Ministry of Environment, Conservation, and Parks."
Imperial said a vac truck has been stationed in the area, as a precaution, to prevent another carryover occurrence.
An all clear was issued just before 4:30 p.m.